No matter how long I leave the gate valves open to drain the black/gray tanks, after a day on the road when I take the main cap off to hook up the slinky, a cup or so of nasty pours out. If I leave the cap off with no hose, and fill the tanks, nothing leaks out for long periods afterward, so I'm pretty sure the gate valves do not leak. So it looks like unavoidable remainders in the plumbing after the gates.
I see only three alternatives:
1. Leave the cap off, so it dribbles on the road as I travel. Not great, but there isn't much and it would be widely distributed.
2. Catch it in a small bucket/basin and pour into the toilet when setting up.
3. Just make a puddle at the site and let it dry - but that seems bad considering all the other people before and after who will also use the site.
How common is this, and what do you do?
2012 Ford F-150 Eco, Max/Max
Jayco 26.5 RLS, Reese Sidewinder